During the process for manufacturing a semiconductor, the dielectric layer can be formed by deposition or non-deposition (e.g. thermal oxidation). For depositing the dielectric layer, there are many methods ranging from the early evaporation to the present physical vapor deposition (PVD) and chemical vapor deposition (CVD), among which the chemical vapor deposition is especially universal. The chemical vapor deposition can be classified into atmospheric pressure chemical vapor deposition (APCVD), sub-atmospheric pressure chemical vapor deposition (SACVD), low pressure chemical vapor deposition (LPCVD), and plasma enhanced chemical vapor deposition (PECVD). The major source of reaction gas containing silicon is silane (SiH.sub.4) or tetra-ethylortho-silicate (TEOS).
For example, the dielectric layer, formed by low pressure chemical vapor deposition (LPCVD) using TEOS, is extensively used in the semiconductor device because of its good step coverage. However, it is graduately replaced by plasma enhanced chemical vapor deposition (PECVD) (at 400.degree. C.) due to its requirement of high reaction temperature (650.degree..about.750.degree. C.). On the other hand, during the process of the atmospheric pressure chemical vapor deposition (APCVD) using TEOS, the reaction can proceed at low temperature by introducing ozone.
Nevertheless, there are surface charge residues resulting from ion bombardment after the process of conventional PECVD using TEOS. It leads to an uneven deposition rate during the following process of APCVD or SACVD using TEOS and ozone so that the deposition thickness of the dielectric layer on the wafer varies with the distance to the center of the wafer, resulting in the difficulty with its following process.